Electroacoustic device



July 15, 1930.

J. P. MINTON El AL ELECTROACOUSTIC DEVI CE Filed Feb. 23, 1924 2 Sheets-Shet 1 max nvemtozs JOHN PRESTON MINTON July 15, 1930. J MINTQN El AL 1,770,491

ELECTROACOUSTI C DEVI CE Filed Feb. 23, 1924 v 2 Sheets-Sheet 2 #13 Mi- #6 /43 141 116116 as 11.9114 116 11;

6 z i 4 I I 7 j avwcwcozs JOHN PRESTON M NTON ABRHHHIVI 5. KINGEL @51 (heir abtozwm Patented duly l5, l93

J'GHN PRESTON MINTfiN, 01" WHITE PLAINS, AND ABRAHAM S. BINGM, OF BROOKLYN, NEW YORK, ASSIGNOBS TO RADIO GQBPOE'ATION B AMERIGA, A CORPORATION DELAWARE ELECTROACQUSTIC DEVECE dncers.

Heretofore it has been the practice to provide loud speakers with onlyone vibratory.

element having a natural resonant frequency equal to the frequency of a note located substentially in the middle of the scale of notes it is desired to he With such on arrange ment the middle notes of the scale are reproduced with suficient cleerness and volume;

but the lower and higher notes are notv reproduced with volume. 1

@ne of the principal objects of our invention is to increase the cle erness and volume of all of the audible notes reproduced by a loud speaker and particularly the notes in suficient clearness end i the higher and lower registers.

Other objects of, our invention are the elimination of interferences between the various reproducing elements incorporated in our loud speaker; and independent regu lotion of volume of sound emanating rltrorn the various sound reproducing elements.

@ther ohiects of the invention will appear from the following description of our inven tion telren in connection with the eccompsnying drawings in which Fig. 1 is e cross section view of one modification of our invention;

Fig. 2 is a plan View of the mechanism for actuating the disphregms;

Fig. 3 is across section view of another modification of our invention;

Fig. i is e plan view of the mechanism for actuating the disphregms;

Fig. 5 is e schematic disgrem ofelectricel connections.

Referring to Fig. l, the central member A comprises a middle vertical ortion 1 having it middle passage-way 2 on two outwardly extending portions 3 and l. The portions 3 and 4 have internal passage-ways 5 end 6 respectively communicating with the middle passage-wiry 2. The outward extremities of the outwardly extending portions are externally threaded for a. purpose to be later described. The upper end of the vertical portion 1 has a peripheral internal shoulder 7 formed in it for limiting the downward movement of a. horn 8, which is held in trictionel enga erment in the vertical portion of the central -nember.

As the low and high frequency units B and C are substantially the same, except as to size, the diameter of the diaphragm of the low frequency unit being larger than that of the high frequency unit, a descriptiomoi one will sufiice for both. i

The low frequency unit B comprises en enclosing'cylindrice casing 9 open st its outer end and closed at its inner end by on integral closure member 10 terminating in an internally threaded nipple 11 for engaging the external threads of the outwerdly entending portion 3 for securing the catering 9 theret Casing 9 of the hi hirequency unit C is similarly secured to t e outwardly extending portion 4.

A peripheral shoulder 12 is integrel with the enclosing casing 9 end is contained therein. The low frequency diaphragm 13, con-- structed of appropriate diaphragm materiel is speced ewey from the closure member 10 by resting against the outer surface of the shoulder 12 and is held in engagement therewith by means of a. clamping ring it end screws 15 passing through re -'ster1ng holes in the die hregm end ring an being threeded in the hotly of shoulder 12..

The outer end of the cosine 9 is internally thresded for the reception ct e closure member 16 rnede of some snitcble meteriel such es hress, end heving'sn integral inwerdly extending flange l? esternsll threaded for en gegement with the internsu ly threaded outer end of the enclosing casing.

The diaphragm ectueting mechanism (of which Fig. 2 is e plain view) comprises as substantislly U shaped permsnent magnet 18 suitably secured to the inner surface eat the closure member it. The free ends 28 of the permanent niegnet ere joins nether by magnetic bridging members 21 cei- 22.

The magnetic bridgin members 21, which are composed of a plura ity of similar laminations united together, have two inte al pole pieces 23, 23 extending toward the 'aphragm 13. Magnetizing coils 24, 24 are mounted on said pole pieces and held in place thereon by means of suitable insulated washers 25, 25. The operation of the diahragm actuating mechanism being well own in the art, requires no description here. The leads from the coils 24, 24 and 24', 24 may be brought out'through insulated bushings in the casings 9 and 9 respectively, or through the closure members 16 and 16 respectively, or the leads may be connected to insulated terminals mounted in cas ings 9 and 9 or the closure members 16 and 1 As the specific manner of bringing out these leads formsno part of our invention, it is not deemed necessary to show an means forbringing them out in the drcwm In general, the low' frequency unit is capable of responding only to low frequencies and the high frequency unit only to high frequencies. This, of course, is the condition desired for the elimination of distortion of tone and interference between the units. This condition is obtained in the following manner. The passageways 5 and 6 are so configured as to preventt e passage of high fre' quency sounds and low frequency sounds re spectively therethrough. An undesired low frequency sounds from the high frequency unit are substantially revented from combining with the desired ow fre uency sounds from the low fre uency unit. imilarly, any undesired high irequency sounds from the low frequency unit are substantially prevented from combining with the desired high frequency sounds from the hi h frequency unit. The vibrating element 0 the low frequenc unit may also be suitably proportione and confi ured so as to minimize the production of igh frequency harmonics thereby. Electrical means, described later, are also provided for preventing distortion and interference between the units. All of these various expedients for eliminating distortion and interference between the units may be used singly, all together, win any desired combination.

The volume of tone from either unit may be controlled by adjusting the position of the pole pieces with respect to the diaphragm. This can be done by screwing the closure members 16 and 16' in or out. It is obvious that the volume of tone from one unit may be regulated independent of the volume of tone from the other unit and vice versa.

Referring to Fig. 3, which shows another modification of our invention, the cylindrical base D comprises a lower part 101 and an upper part 102. The lower part 101 has an outwardly extending flange 103 for 1m -a cylinder open at its upper end parting stability to the device and an upwardly extending peripheral shoulder 104.

The upper part 102 of the base D com rises an partially closed at its lower end by the integral circular baflle plate 105 having an opening 106 in its center for a pur to be later described. The u per part as a dependin peripheral shoul er 107 registering wi shoulder 104 of part 101. A low fe uency diaphragm 108 constructed of suitab e diaphra m material is clamped between the two shou ders 104 and 107 by means of counter sunk screws 109 passing through plain holes in shoulder 104 and threaded into re stering holes in shoulder 107. The diap ra m is thus spaced away from part 101 and ba e plate 105 for the establishment of proper acoustic conditions. The parts of base D may be moulded out of brass, aluminum or some suitable alley or may be made by pressing, spinning or any of the other well known methods.

A closure member E, made of brass, aluminum or any suitable alloy, comprises a base portion 110 of annular configuratioman integral upwardly extending cylmdrical por tion 111 terminating in an upwardly extending nipple 112 and an internal annular intewithin the ni p e from the space contained within the cylindrical portion 111.

The diaphragm actuating mechanism F, a plan view of which is shown by Fig. 4, comprises an annular mounting late 114 secured in an annular grove 115 in t e lower surface of base portion 110 by counter sunk screws 116. A rmanent magnet 117 substantially U-shape in configuration is bridged at its extremities or poles by magnetic bridging members 118 and 119 having downwardly extending oles 118' and 119' respectively; and magnet ridging members 120 and 121 having upwardly extending poles 120 and 121 respectively. The permanent magnet, bridging members and non-vibrating non-magnetic circular plate 117 arranged for reventing the passage of sound from the diap ragm 108 thru the annular opening in 114, are secured together and to the annular mounting plate by screws 122. v

Coils 123 are mounted on the various poles 118', 119', 120' and 121 and held thereon by means of insulated washers 124. The leads from the coils may be brought out through insulated bushings 125 or any of the other well known methods in the art.

The downwardly extending poles 118 and 119 together with the coils mounted thereon extend into the opening 106 but do not entirely close the said opening. The ends of the poles are in suitable proximity to the low frequency diaphragm 108 to efiect its operation.

' The annuiarplate 113 is threaded internal- 1 y for the reception of the externally threaded ate 113 se arating the space contained The upwardly extendin nipple 112 has an internal peripheral shoul er 132 at its upper end for limitin the downward movement of a horn 133 within the nipple. The upper end of the nipple is threaded externally for the reception of the threaded flange 134 of the clamping member 135, which has an additional flange 136 engaging a peripheral ledge 137 incorporated in the horn 133 whereby the horn 133 is detachably secured to the closure member E. V

Adjustment of the high frequency diaphragm 129 with respect to the pole pieces 120"and 121 is obtained by the following arrangement. The upper surface of nipple 126 is bevelled and bevelled teeth out therein as shown at 138. These teeth are in engagement with teeth of bevel gear 139 fastened to a shaft 140 which extends through the nipple 112. The shaft 140 is loosely ournaled thru the nipple to permit of some upward and downward motion of gear 139. A knurled knob'141 is secured to the protruding end of shaft 140 by means of a set screw 142. The distance between the high frequency diaphragm 129 and the pole pieces 120" and 121 is thus controlled by turning the knob 141. I

The distance between the low frequency diaphragm 108 and the pole ieces 118' and 119 is adjusted by screwing t e closure member E into or out of the upper part 102 of base D. It is thus obvious that the diaphragms may be adjusted independent of each other.

The fullline arrows indicate the path of the low frequency sound waves produced by the vibration of the low frequency diaphragm 108. These soundwaves pass through that portion of the opening 106 unoccupied by the pole pieces 118;. 119' and the coils 123. through a plurality ofv constricted openings 143 in annular plate 114 and then through another plurality of constricted openings 144 in annular plate ll3 into the horn 133. These openings are so configured as to substantially prevent: 1st--any high frequency sound from the low frequency unit enterin the born or high frequency unit, 2ndany Eigh frequen cy sounds entering the low frequency unit and 3rd-any high frequency sounds emanating from the lower surface of the high frequency diaphragm entering the horn. It is thus seen that distortion of the sbulidemanating from the horn is prevented and interference between the units is substantially eliminated.

Referring to Fig. 5, which is a schematic diagram of electrical connections for our loud speaker, the coils 201 for actuating the low frequency diaphragm are connected in parallel; while the coils 202 for actuating the high frequency diaphragm are also connected in parallel. The coils 201 are connected across the output terminals of electrical filter 205, while the coils 202 are connected across the output terminals of electrical filter 206. The filters 205 and 206 are connected in series across the input leads 203 and 204. The filter 205 has characteristics which permit the passage of low frequency currents corresponding to the low frequency notes thru the coils 201 and prevents the passage of high frequency currents corresponding to the high frequency notes thru the coils 201. The filter 206 has characteristics which permit the passage of high frequency currents corresponding to the comparatively high frequency notes thru the coils 202- and prevents the passage of low frequenc currents corresponding to the comparative y low frequency notes thru the coils 202. It is thus seen that we provide electrical means for preventing distortion and interference between the low frequency unit and .the high frequency unit.

In order for the coils of a loud speaker to be actuated by maximum energy volume of sound produced there y is a maximum it is necessary that the impedance of the coils be as nearl equal to the impedance of the tube to whic they are connected as it is possible to make them. The high frequency,

coils 202 are so designed that this impedance is substantially equal to the impedance of the tube at a frequency which occupies a middle osition in the scale of notes of comparative y higher frequencies.

Similarly, we arrange the coils 201 of the low frequency unit to have an impedance substantial y equal to the impedance of the tube over the lower range of frequencies to which the low frequency unit is responsive. This will require more turns on the coils 201, which will give them a fairly high inductance. At the high frequencies the impedance of coils 201 will become excessively high and thus tend to prevent passage of high frequency energy to the coils 202. The connection of the filter 205 to the coils 201. however, permits the free passage of high frequency currents thru the coils 202 so that the impedance of the entire system at the higher frequencies is largely determined by the impedance of coils 202. The impedance of the high frequency coils 202 is sufficiently low at the low frequencies, so as not to appreciably influence the total impedance of the system. Thus a substantially constant impedance for the electro-acoustic system equal to the impedance of the tube is obtained over so that the nected to said first filter, and a second electromagnetic reproducer havin a coil connected to said second filter, the impedance of said coils being substantially equal to the impedance of said amplifier over the range 70 w of -audible frequencies.

JOHN P. MINTON. ABRAHAM S. RINGEL.

ries as shown, without departing from the a spirit of the invention. In fact, the coils might be connected in a number of different ways without departing from the scope of the invention.

\Vhile we have shown only two sound reproduction units, we do not wish to be limited to such a number, but may employ as many as the results to be accomplished should demand.

\Vhile our invention is shown and described in connection with sound reproducers of the loud speaker variety, we do not limit ourselves to such devices but may also employ the principle of a plurality of diaphragms or vibrating elements having different resonant frequencies in various types of sound transmitters and sound receivers.

While we have shown and described various referred modifications of our invention, we 0 not'limit ourselves to said modifications; but may employ such other embodiments as may come within the spirit and sco of our invention.

aving described our invention, what we claim is:

1. The combination of an audio frequency generator, an acoustic device, a plurality of electro-acoustic devices, each having a coil, each of said coils being responsive to a characteristic vibration fre uency and having an in) edance substantially equal to the impe ance of the generator at the respective vibration frequency of each coil, whereby maximum value of sound is produced.

2. In combination a plurality of electroacoustic devices having different size diaphragms each of said electro-acoustic'. devices being provided with separate passages constructed selectively to conductseparate vibration frequencies, and a single acoustic device through which such se arate vibration frequencies are transmitte 3. In combination, a vacuum tube amplifier having an output circuit, a plurality of electro-magnetic reproducers connected to said output circuit, each of said reproducers having a coil and the impedance of said coils being substantially equal to the impedance of said vacuum tube over the range of -ireuencies for which said reproducers are designed to operate.

4. In combination, a vacuum tube amplifier having an output circuit, a first filter connected to said output circuit, a second filter connected to said output circuit, a first electro-magnetic reproducer having a coil con- 

